...behold, each one follows the dictates of his own evil heart, so that no one listens to Me. (Jeremiah 16:12)
An evil heart is any heart void of the Spirit of God. Our hearts without Christ are wicked and deceptive. The prophet Jeremiah also said, “The heart is deceitful above all things, and desperately wicked; who can know it?”(1)
Therefore, we need a foundation, a benchmark to guide our hearts and minds. That foundation is the Word of God. No matter how the heart directs, the Spirit and the Word must lead it. If not, it will eventually lead us astray. For example, with regard to adultery, the heart may tell you that you are in love, but the Word of God and the Spirit of God will tell you, no, you are in lust.
We are to listen to God above our hearts. A heart for God listens to Him. Therefore if you find yourself attempting to justify yourself according to the dictates of your heart, you most likely have an evil heart. The heart must be adjusted to the Spirit and the Word, never the reverse.